Product Core Brief

• Model: SPAD346C
• Brand: ABB
• Series: ABB SPAD protection relay family (biased differential relay)
• Core Function: Integrated transformer protection relay combining three-phase biased differential protection, overcurrent protection, and earth-fault protection for dual-winding transformers and generator-transformer units.
• Product Type: Transformer differential protection relay
• Key Specs: 1 A / 5 A CT input | 80–265 V auxiliary supply | 4 trip + 4 signal outputs | 5 programmable inputs | CBFP | Disturbance recorder | Legacy ABB component
• Condition: New Original / New Surplus (verify by full order code and revision)

Key Technical Specifications

• Part Number:
• Product Type: Biased differential protection relay for transformers
• System Role: Protects dual-winding transformers, generator-transformer units, and (with limitations) three-winding transformers against winding short circuits, inter-turn faults, earth faults, and overcurrent conditions
• Internal Modules: SPCD 3D53 (three-phase biased differential), SPCD 2D55 (earth-fault), SPCJ 4D28 (combined overcurrent + earth-fault), SPTR 9B31 (I/O relay), SPGU 240A1 or equivalent power supply module
• CT Rated Current: 1 A or 5 A (selectable per side; HV and LV may use different ratings)
• Auxiliary Supply Voltage: 80–265 V AC/DC (verify against nameplate)
• Frequency: 50/60 Hz
• Outputs: 4 trip relays + 4 signal relays (heavy-duty)
• Inputs: 5 programmable external control inputs for gas relay, oil temperature, and other transformer auxiliary signals
• Protection Features: Biased differential with 2nd-harmonic inrush blocking and 5th-harmonic overexcitation blocking; three-stage overcurrent; two-stage earth-fault backup; CBFP (circuit breaker failure protection); phase unbalance detection
• Disturbance Recorder: Integrated disturbance recorder for current and digital signal capture
• Mounting: Panel-mounted relay (verify exact cutout and depth against OEM documentation)
• Lifecycle Status: Legacy component; verify current ABB lifecycle phase before long-term deployment

 

Product Introduction (No Fluff)

The ABB SPAD346C is an integrated transformer protection relay that combines three-phase biased differential protection, overcurrent protection, and earth-fault protection in a single unit. It is designed primarily for dual-winding transformers and generator-transformer arrangements, and can also be applied to three-winding transformers when at least 75% of the short-circuit power comes from one direction.

Its practical value is maintaining legacy ABB substation and transformer protection schemes where a failed relay can leave critical assets without differential protection. The relay supports digital vector group matching and CT ratio correction, eliminating the need for interposing CTs in many dual-winding transformer applications. For maintenance replacements, the exact revision and suffix (e.g., SPAD346C3) should be matched against the existing relay label, since auxiliary voltage, I/O configuration, and communication options may differ across variants.

 

QA & Testing SOP (Dynamic & Transparent)

For legacy protection relays, we verify mechanical integrity and basic readiness before shipping.

1. Part number verification — Confirm SPAD346C and the full suffix (e.g., C3) on the label; check auxiliary voltage and serial number.
2. Visual inspection — Inspect the front panel, display, connectors, terminal blocks, and mounting clips for corrosion, burn marks, or mechanical damage.
3. Connector and terminal check — Verify CT input terminals, trip/signal output terminals, and auxiliary supply terminals for oxidation, loose contacts, or contamination.
4. Insulation and short-circuit check — Confirm no short circuits between CT inputs, auxiliary supply, and output circuits before energizing.
5. Power-up verification — Where test fixtures are available, apply rated auxiliary voltage and verify display, LED indicators, relay self-test, and output operation; pack with terminal protection.

 

Installation Pitfalls & Guide (Engineer to Engineer)

❗ Match the full order code. SPAD346C variants (e.g., SPAD346C3) may differ in auxiliary voltage, I/O configuration, or communication options. Substituting without verification can cause wiring or compatibility mismatches.

❗ Verify CT polarity and vector group. Incorrect CT polarity or vector group settings can cause false differential trips or failure to operate during internal faults.

❗ Confirm auxiliary supply voltage. The relay supports a wide auxiliary voltage range, but the actual unit may be configured for a specific range. Verify against the nameplate before energizing.

❗ Back up relay settings. Before replacement, record all protection settings, including differential slope, pickup values, time delays, harmonic blocking thresholds, and CBFP timing.

❗ Test with secondary injection. After installation, verify differential protection, overcurrent stages, earth-fault stages, CBFP, and trip/signal outputs using secondary injection testing before returning the transformer to service.

❗ Check disturbance recorder configuration. Confirm trigger conditions and recording parameters if post-fault analysis capability is required.

Replacement steps:

1. Record all relay settings, CT ratios, vector group, and wiring connections.
2. Remove auxiliary supply and verify zero voltage before disconnecting CT and trip circuits.
3. Install the replacement SPAD346C with the same full order code and restore all settings.
4. Apply auxiliary supply, verify self-test, and perform secondary injection testing on all protection functions.

 

Technical FAQ

What does the SPAD346C do? It is an integrated transformer protection relay combining three-phase biased differential, overcurrent, and earth-fault protection for dual-winding transformers and generator-transformer units.

What is the difference between SPAD346C and SPAD346C3? SPAD346C3 is a variant within the SPAD346C family. The suffix may indicate differences in auxiliary voltage, I/O configuration, or communication options. The nameplate should always be confirmed before ordering.

Can it protect three-winding transformers? Yes, but only when at least 75% of the short-circuit power comes from one direction.

Does it support disturbance recording? Yes. It includes an integrated disturbance recorder for capturing current and digital signal waveforms during faults.

Is it still available? It is considered a legacy component. New surplus and verified replacements can be sourced, but long-term projects should evaluate migration to a supported ABB protection relay platform.